Downhole burner for wells



March 22, 1966 H. BRANDT ETAL DWNHOLE BURNER FOR WELLS 3 Sheets-Sheet 1LFiled June 27, 1963 March 22, 1966 H. BRANDT ETAL DOWNHOLE BURNER FORWELLS 5 Sheets-Sheet 2 Filed June 27, 1963 FIG. 6A

March 22, 1966 H. BRANDT ET AL 3,241,615

DOWNHOLE BURNER FOR WELLS Filed June 27, 1963 5 Sheets-Sheet 5 INVENTORSHARRY BRANDT HERBERT R. HAZARD MMELL J N D. HU

. SCHULZ United States Patent O 3,241,615 DOWNHOLE BURNER FOR WELLSHarry Brandt, Whittier, Calif., and Herbert R. Hazard, Columbus, .I h11D. Hummell, Brice, and Earl J. Schulz, Columbus, Ohio, assiguors, bydirect and mesne assignments, to Chevron Research Company, a corporationof Delaware Filed .lune 27, 1963, Ser. No. 291,126 Claims. (Cl. 166-59)This invention relates to downhole gas and air burners for use in wellsto stimulate production therefrom and more particularly this inventionrelates to improved apparatus for supplying a combustible mixture to thecombustion chamber of a downhole burner.

As known in the petroleum producing art, production from a well can beimproved by heating the fluids such as oil in the well and in theadjacent producing formation. Heretofore there have been many methods ofheating fluids in a petroleum-bearing formation penetrated by a well.The most successful of the methods includes burning a combustiblemixture in a downhole burner. Examples of downhole gas and air burnersare shown in U.S. Patents 2,887,160 and 2,895,555. Generally, downholeburners comprise a combustion chamber having an exhaust section, anignition means and a means for supplying a combustible mixture to thecombustion chamber.

Briefly, the present invention is directed to improved apparatus forsupplying a combustible mixture to the combustion chamber of a downholeburner. In a broad aspect this invention provides an improved deliverytube means for directing a combustible mixture to a combustion chamber.The delivery tube means includes a flashback prevention means and acheck valve means for controlling the iiow of combustible mixture intothe combustion chamber. The delivery tube means directs the combustiblemixture from the gas and air supply means to the combustion chamber ofthe downhole burner. The

flashback prevention means are positioned in the delivery tube meansnear the combustion chamber to prevent combustion from flashing up thegas and air supply tube means. The flashback prevention means functionto prevent ashback up the tubing in a manner which does not causeexcessive pressure drop in the supply system which would greatlyincrease compression costs. Flashback preventers of the presentinvention comprise a porous material having restricted flow pathstherethrough. The check valve means controls the flow of combustiblemixture to the combustion chamber and prevents undesirable pulsatingflow through the combustion chamber and the delivery tube means. Thecheck valve means is positioned in the delivery tube means above thecombustion chamber and prevents the backflow of gases through the tubemeans which otherwise could result in a pressure pulse during ignition.The check valve means traps gas in the burner combustion chamber onshutdown and thereby aids in preventing flooding of the combustionchamber by well uids.

It is a principal object of the present invention to provide an improvedcombustible gas and air delivery tube means for supplying a combustiblemixture to the combustion chamber of a downhole burner.

Further objects and advantages of the present invention will be apparentfrom the following detailed description read in light of theaccompanying drawings which are a part of this specification.

FIG. l is a diagrammatic view illustrating apparatus assembled inaccordance with the present invention positioned in a well.

FIG. 2 is a longitudinal view with portions broken away for clarity ofpresentation and illustrates the pre- 0 ferred embodiment of apparatusof the present 1nvent1on. 7

FIG. 3 is section 3-3 of FIG. 2.

FIG. 4 is an enlarged sectional view of a portion of the preferredembodiment of apparatus and illustrates a means for preventingflashback.

FIG. 5 is section 5-5 of FIG. 4.

FIG. 6 is a graph showing the relationship of ow velocity to exit gap toprevent flashback according to the present invention.

FIG. 6A is an isometric view of a simple test device useful in selectingflashback prevention means in accordance with this invention.

FIG. 7 is a greatly enlarged sectional view illustrating an alternativemeans for preventing llashback.

FIG. 8 is section 8 8 of FIG. 7.

FIG. 1 which is useful in understanding the present invention shows anearth formation penetrated by well 71. A downhole gas-air burner,represented generally by 40, is shown in the well 71. The burner 40 islocated in a position to cause maximum allowable heat transfer to thefluids in well 71 and to oil-bearing formation 72. The burner isconnected to a supply of combustible mixture by means of tubing 53. Acombustible gas and air mixture is provided for flow through tubing 53by any suitable means. For example, a combustible gas and air mixturemay be supplied for How through tubing 53 from a gas source 74 and anair source 75 through valves 76 and 78 and conduits 77 and 79. A methodand apparatus for controlling the flow of gas-air mixture to a downholeburner is described and claimed in U.S. Patent 3,012,607.

The burner 40 may include an exhaust section 44 connected to acombustion chamber section 42 to receive exhaust gas from the combustionchamber inside combustion chamber section 42. Burner head section 43contains the burner ignition means and controls the How of gas and airto the combustion chamber section 42. A tubing connecting means, whichmay be for example a tubing collar 47, connects the burner head section43 to the combustible mixture tubing 53.

As shown in FIG. 1 the downhole gas and air burner 40 is located in awell 71 adjacent a producing formation 72. The burner is ignited bysuitable means such as an electrical ignition means supplied byelectrical source 73, and combustion occurs in combustion chambersection 42. The heat given off to the surrounding formation 72 improvesthe viscosity and mobility of the oil in formation 72 thereby making itmore easily recovered by conventional means. gas and air burner of thepresent invention may be positioned with a conventional pump and suckerrod string in the borehole and the less viscous oil pumped to thesurface. In addition to improving the mobility of the oil, the downholeburner of the present invention is also useful in increasing solubilityof various oil constituents such as waxes and asphaltenes, thusimproving recovery.

The downhole burner of the present invention is adapted to be positionedin a well up to many thousands of feet beneath the earths surface;therefore the apparatus must be reliable in operation since it is adifficult and expensive procedure to remove the burner from the hole toclean it or to make minor repairs. It is also highly desirable that onlya single conduit be used to supply both gas and air to the burner. Thusa combustible mixture must be flowed through many feet of tubing fromthe surface to` the burner.

In a broad aspect the present invention includes delivery tube means forflowing a combustible mixture to the combustion chamber of a downholegas and air burner, said tube means having check valve meansincorporated therein and located near the entry port into the combustionchamber, which check valve means allows fluid flow through said tubemeans to the combustion chamber but does not For example, the downholepermit fluid flow from the combustion chamber up through said tubemeans. It has been found that locating the check valve means above thecombustion chamber and in the delivery tube means insures that the checkvalve means will be operable under difiicult conditions including thepresence of dirt or unconsolidated particles in the well. Flashbackprevention means are positioned in the delivery tube means to preventcombustion from flashing up the delivery tube means.

FIG. 2 shows a longitudinal view with portions broken away to showapparatus of the preferred embodiment of the present invention. FIG. 3is a sectional view talccn at line 3 3 of FIG. 2. The downhole burnerrepresented generally by the numeral itl includes a combustion chambersection 42 having an exhaust section A for receiving exhaust gases atits lower end. The combustion chamber section 42 preferably has aceramic liner 5f) which forms the combustion chamber 52. Entry portmeans, such as ports 54 and 55 are provided in the ceramic liner 50 toallow a combustible mixture to flow into the combustion chamber 52.Ignition means, such as glow plug 56, having a glow element 59, aremounted by suitable means 57 in operable relationship with thecombustion chamber 52 and entry port means 5d and 55 so as to ignite acombustible mixture passing into the combustion chamber 52. Suitableelectrical connection between a source of electricity and the glow plug:6 is provided by insulated cable 58 and the tubing 53. The downholeburner is connected to the tubing 53 by suitable means such as themating threads 6@ on collar 47. The tubing forms a flow path for gas andair from the surface to the downhole burner 4t).

A burner head section @i3 closes off the upper end of the combustionchamber 5d. The glow element of glow plug 56 is located in a recess ofthe burner head section 43 in fluid communication with the combustioncharnber. A fluid-tight seal at 51 prevents fluid ow up the glow plugtaphole.

Fluid flow means through the burner head section d3 provide forcommunication to the combustion chamber 52 through the entry ports 54and 55 therein. Flow paths such as shown by numerals 61 and 62 areprovided in the burner head section 43. Flashback prevention means,indicated generally by 64 and 65, are located in suitable inserts 68 and69 in the fiow paths 61 and 62.

Tube means, indicated generally by the numeral 3f), direct the flow ofcombustible mixture to the flow paths 61 and 62 to the combustionchamber. The tube means are connected to the flow paths 6l and 62 in afluid-tight manner and provide therewith a means for flowing combustiblemixture from a surface supply conduit such as Conduit 53 to thecombustion chamber 52 of the downhole burner.

A tube having an open end 3l provides for fluid flow from the interiorof gas and air supply conduit 53 to combustion chamber 52. The tube 30is formed in a U-shaped configuration and the open end is located nearthe floor 32 of the burner head section 43. The combustible gaseousmixture which is flowed down the well in the tubing 53 to a positionabove the combustion chamber is thus caused to flow in substantially theopposite direction for a short distance prior to flowing to thecombustion chamber. When there are exposed electrical connectionsextending above the burner head section, such as the glow plug 56 andelectrical cable 53, it is desirable to locate the open end 31 of tubemeans 30 below the level of the exposed electrical apparatus. In thismanner any 4accumulated Water or brine can be cleared from the gas-airchamber by means of pressure in conduit 53. Short circuiting of theelectrical apparatus as a result of wet connection is therefore notlikely to occur.

The tube means 30 may be divided so as to flow gas and air to more thanone combustion chamber entry port. For example, -a pair of tubes 33 and34 having common openings into tube 3@ can flow gas and air to entryports 54 and 55. Obviously one or more entry ports can be used.

A check valve means indicated generally by the number titl is positionedin the flow line of tube means 3). The check valve means il@ is locatednear the entry ports 54 and 55. That is to say that the check valvemeans should be within a few feet of the entry port means as compared tolength of the supply conduit 53 which may be up to 5G00 feet or more inlength. The Check valve means allows fiuid flow from the supply conduit53 through tube means 3@ and into combustion chamber 52 and preventsflow from the combustion chamber 52 through tube means 30 into thesupply conduit 53. It has been found that locating the check valve meansin the combustible mixture delivery tube means 3) above the combustionchamber serves multiple purposes. The check valve means prevents thebacliow of gases through the tube means which could result in a pressurepulse during ignition and, also, the check valve means traps gas in theburner combustion chamber on shutdown and thereby aids in preventingflooding of the combustion chamber by well fluids.

A further and particularly important advantage gained by locating thecheck valve means above the combustion chamber is that the pressure ofthe combustible mixture in the supply tubing is higher than the pressurein the combustion chamber. This is important because a pulsation ofpressure in the combustion chamber can occur; as for example when thelevel of fluids in the well changes, the pressure in the combustionchamber will change. lf no check valve is present, flow of the gas andair mixture into the combustion chamber might stop temporarily until thesurface gas and air mixing equipment reacts to the change in pressure tosupply the combustible mixture at the higher pressure. The presence of acheck valve means having a pressure drop of as little as l p.s.i.insures that the supply tubing 53 is always filled with a Combustiblemixture that is at from l-S p.s.i. higher pressure than the pressure inthe combustion chamber. Thus where a pressure surge occurs in the well,the combustible mixture will continue to be supplied. A pressuredifferential of from 1-5 p.s.i. has been found adequate for mostoperations. Ir" desired for special circumstances where large pressuresurges are encountered, a check valve having a higher pressure drop canbe installed and the pressure differential increased.

Thus the mixture is flowed to a first position which is immediatelyabove the combustion chamber, for example the space defined by tubingconnecting collar 47. The .mixture is then flowed to the combustionchamber through check valve means 80. Thus the mixture is at a higherpressure at the first position than the pressure prevailing in thecombustion chamber. As noted above, this pressure differential ispreferably from 1 to 5 p.s.i. Means providing a pressure differentialmay take other forms than the check valve means. For example, a plug ofporous material can be positioned across the gaseous flow conduit tocause a desirable pressure differential to exist between the supplytubing and the combustion chamber. When the pressure in the combustionchamber increases a limited amount there will be some incrementalpressure available in the supply tubing to maintain partial ow of thecombustible mixture into the chamber at least until the surface pumpingequipment senses the pressure surge and corrects for it.

The check valve means functions to allow flow in only one directionthrough the tube means 30. A suitable valve means includes a housing S1having a flow path through its entire length. Means movable, such asball 82, are provided in the flow path. A resilient means such ascompression spring is provided to normally urge the ball into a seatformed by O-ring 33 to close the flow path to fluid flow. The spring maybe overcome by a differential pressure in one direction to allow lgasand air to flow through the tube means 3() into the comon bustionchamber 52. The differential pressure is preferably 1 5 p.s.i. As isevident, a differential pressure acting with the force of the spring 65closes the flow path through the check valve to fluid flow. There arecommercially available check valve means which function adequately inthe present invention.

In llowing a combustible mixture to thev combustion chamber of a burnerwhere it is combusted, the danger of flashback up the combustiblemixture conduit must be minimized. For example, when the mixture isbeing combusted and for some reason a pressure surge occurs or the flowof gas and air from the surface is temporarily halted, the flame can,unless prevented by some means, flash up the supply line and perhapscause serious damage. Therefore there is a need for flashback preventionmeans which will function to prevent flashback up the tubing and whichwill not cause an excessive pressure drop in the supply system whichwould greatly increase compression costs. Flashback preventers of thepresent invention comprise a porous material having restricted flowpaths therethrough. The porous material is preferably a porous metalhaving a maximum pore size of about .004 inch in diameter. It has beenfound that at normal minimum operating Ipressure of a downhole burner,for example, 2.50 p.s.i., a flame can flash back through a hole largerthan .004 inch with a stoichiometric methane-air mixture. That is, astoichiometric mixture of methane and air will not ash back throughrestricted openings less than 0.004 inch in diameter at pressures lessthan 250 p.s.i. Particular size openings will vary for different gasesand pressures and an adjustment can be made for the particular gas usedand maximum pressure expected.

With reference to FIG. 4 and FIG. 5 flashback preventer means inaccordance with the present invention are shown. A thin sheet of porousmaterial 64 is :provided inthe flow path 61 to the combustion chamber ofthe burner. The sheet is mounted diagonally across the ilow path. It hasbeen found that porous material having openings of less than .00 willprevent flashback when a combustible mixture of methane and air is usedat a pressure of 250 p.s.i. or less. However, when a thin wall of .004inch material is used, the flame on the downstream side of the wall mayeventually heat the upstream side of the wall to the ignitiontemperature of the combustible mixture and ignition of the mixtureupstream can result, causing flashback of the flame up the conduit.Since it is highly desirable to use a thin wall of porous material 4tokeep the pressure drop as low as possible, it is a particular feature ofthis invention to mount the porous material diagonally across the owpath. By mounting the porous metal diagonally across the flow path, acomponent of gaseous mixture flowing through the porous wall is causedto flow parallel or nearly parallel to the downstream side of the porousmaterial and thus blows the flame olf the downstream Wall. In thismanner a relatively thin porous sheet or wall, for example, 1/16 `of aninch thick can be used as a flashback preventer. Using a thin porouswall is important because of the lower pressure drop across the thinwall compared to the pressure drop across a thick piece of porousmaterial which would be necessary if the porous material were maintainednormal -or near normal to the center line of the delivery tube. Forexample, a suitable porous metal is porous stainless steel, Type 316,Grade D, lAG" thick, and manufactured by Micro Metallic Corp. of GlenCove, N.Y. In the preferred embodiment the flashback preventer ismounted in a manner to form an acute an-gle with the center line of thedelivery tube of about to 35. The component of ilow parallel to theunderside of the porous metal surface must be of a suitable magnitude tobloW the llame .off the surface. The flashback preventers comprise aporous material positioned in the combustible mixture flow path so thatany llame that is propagated on the `downstream side ofthe surface willbe blown off the surface.

The ashback preventers are positioned across the combustible mixturellow path and have a downstream side which makes a determinable anglewith the center line of flow to cause at least a portion of the flowingmixture to flow along the downstream side. A depending conically shapedflashback preventer formed of porous material and forming thepredeterminable angle with the flow path` of the mixture is also -usefulin the presen-t invention. This alternative arrangement of ashbackpreventer means is illustrated in FIGS. 7 and 8. As there shown, aconically-shaped ilashback preventer 94 is positioned in the combustiblemixtu-re flow path 91 which is formed by appropriate tubes 98 and 99.The conically shaped flashback preventer 94` may be positioned betweenthe pair of tubes 98 and 99 and held in place by meansy of a weld 90. Instill a further embodiment a thin walled cylindrical or bar-like porousmaterial element can be used when the wall of the conduit which formsthe tlow path is tapered to form the desired angle with the downstreamsurface of the porous element to insure a component of liowsubstantially parallel to the downstream surface.

With reference to FIG. 6 and FIG. 6A, curves of the velocity and flowrequired to blow llame transversely off a porous metal strip of the typeused in the preferred embodiment of apparatus plotted against the exitgap and a simple device to obtainV the information in the curves areshown. The apparatus shown in FIG. 6A comprises a simple box 21 havingan entry port 23. A tube 22 is connected to the entry port 23 to allow acombustible mixture to be flowed into the Ilower portion of box 21. Asshown in FIG. 6A a porous metal strip Z4 is mounted across the box. Oneend 25 of the box,` which end is analogous to the exit gap of FIG. 6, isopened above the metal strip 24 for gas flow through the metal strip andout yof the box. Thus a combustible mixture can be flowed into the boxthen through the metal strip and finally out of the box. The mixture isignited at end 2S of the box and the flow rate and velocity can beadjusted to cause the flame to be blown transversely off the strip todetermine points `on the curves in FIG. 6. The exit gap 25 is adjustedto get a varietyof points. This data is incorporated into the design offlashback preventers for use in borehole heaters, which flashbackpreventers comprise porous material set in the combustible mixture flowpath in such a manner that any llame that is propagated on theundersurface of the material will be blown off the surface.

It is apparent that modifications other than those described herein maybe made to the apparatus of this invention without departing from theinventive concept. It is intended that the invention embrace allequivalents within the scope of the appended claims.

We claim:

1. Apparatus for burning a combustible mixture in a well comprising acombustion chamber means having an exhaust means at its lower end, means`for positioning said combustion chamber means in a well, entry portmeans in the upper portion of said combustion chamber means, ignitionmeans for igniting a combustible mixture in said combustion chambermeans, tube means for flowing a combustible mixture down the Well andinto said combustion chamber means, said tube means communicating withsaid combustion chamber means through said entry port means, check valvemeans in said tube means above said entry port means and flashbackprevention means in said tube means between said check valve means andsaid entry port means.

2. Apparatus for burning a combustible mixture in a well comprising acombustion chamber means having an exhaust means in the lower portionand entry port means in the upper portion, means for suspending saidcombustion chamber means in a well, means closing off the upper portionof said combustion chamber means, tube means communicating with saidentry port means and forming therewith the only flow path through saidclosing means for flowing a combustible mixture to said combustionchamber means lthrough said entry port means, well pipe means for owinga combustible mixture down the well to said tube means, check valvemeans in said tube means above said entry port means for controlling oWthrough said tube means to said combustion chamber means, said checkvalve means allowing i'low only through said tube means into saidcombustion chamber means, and ashback prevention means in said tubemeans between said check valve means and said entry port means.

3. Well burner `apparatus comprising a combustion chamber meanspositioned in a well and having an exhaust means, entry port means insaid combustion chamber means as the only entry for combustible mixtureinto said combustion chamber means, ignition means to ignite acombustible mixture passing into said combustion chamber means, ow meanscommunicating with said combustion chamber means through said entry portmeans, well pipe means extending from the surface down the well andcommunicating with said ow means for supplying combustible mixture tosaid ow means, lashback preventer means in said ilow means, saidflashback preventer means comprising porous material positioned in saidflow means, said porous material having a downstream surface forming apredetermined acute angle with the centerline of said flow means wherebya component of the combustible mixture flow is caused to flowsubstantially parallel to the downstream surface of said porous materialto blow flame off the downstream surface of said porous material.

4. The apparatus of claim 3 where the predetermined acute angle isbetween 25 and 35.

5. The apparatus of claim 3 Where the porous material is thin porousmetal.

6. The apparatus of claim 5 further characterized in that the porousmetal is a fiat strip positioned in said flow means.

7. The apparatus of claim 5 where the porous metal is conically shapedand is positioned in said ow rpath.

8. Apparatus for burning a combustible mixture in a well comprising acombustion chamber means having exhaust means at its lower end, meansclosing 01T the upper end of said combustion chamber means, entry portmeans in the upper end of said combustion chamber means for flowing acombustible mixture into said combustion chamber means, electricalignition means in said combustion chamber means in operable relationshipwith said entry port means to ignite a combustible mixture flowing intosaid combustion chamber means, said ignition means having electricalconnections extending above said combustion chamber means and throughsaid means closing off the upper end of said combustion chamber means,tube means extending through Said means closing off the upper end ofsaid combustion chamber' means and communicating with said ent-ry portmeans, said tube means including a conduit extending above said meansclosing olf said combustion chamber means and having substantially abend and terminating above said means closing ol said combustion chambermeans and below the level of the portion of said electrical connectionsextending above said means closing off said combustion chamber means.

9. Apparatus as in claim 8 further characterized by a check valve meansin said tube means.

10. Apparatus as in claim 8 further characterized by ashback preventermeans in said tube means.

References Cited by the Examiner UNITED STATES PATENTS 1,041,863 10/1912Oehlke 158-112 1,368,120 2/1921 Cole 158-112 1,420,405 6/1922 Beler158-112 1,620,071 3/1927 Chappelle 158-112 2,618,540 11/1952 Teti158-112 2,680,487 5/1954 Carpenter 166-59 X 2,810,631 10/1957 Kanenbley158-112 X 2,913,050 1l/1959 Crawford 166-39 X 3,070,178 12/1962 Grahamet al 166-59 X 3,072,189 1/1963 MacSporran 166-59 X 3,107,728 10/1963Kehn 166-39 X CHARLES E. OCONNELL, Primary Examiner.

BENJAMIN HERSH, Examiner.

1. APPARATUS FOR BURNING A COMBUSTIBLE MIXTURE IN A WELL COMPRISING ACOMBUSTION CHAMBER MEANS HAVING AN EXHAUST MEANS AT ITS LOWER END, MEANSFOR POSITIONING SAID COMBUSTION CHAMBER MEANS IN A WELL, ENTRY PORTMEANS IN THE UPPER PORTION OF SAID COMBUSTION CHAMBER MEANS, IGNITIONMEANS FOR IGNITING A COMBUSTIBLE MIXTURE IN SAID COMBUSTION CHAMBERMEANS, TUBE MEANS FOR FLOWING A COMBUSTIBLE MIXTURE DOWN THE WALL ANDINTO SAID COMBUSTION CHAMBER MEANS, SAID TUBE MEANS COMMUNICATING WITHSAID COMBUSTION CHAMBER MEANS THROUGH SAID ENTRY PORT MEANS, CHECK VALVEMEANS IN SAID TUBE MEANS ABOVE SAID ENTRY PORT MEANS AND FLASHBACKPREVENTION MEANS IN SAID TUBE MEANS BETWEEN SAID CHECK VALVE MEANS ANDSAID ENTRY PORT MEANS.